replace Meson version check with a specification-compliant version comparator

The current check compares the integers split out from `meson --version`
one by one. This is an ad-hoc version comparison algorithm with a few
flaws, notably that it doesn't truly understand how version components
fit together, and that broke once Meson bumped the major version. There
are other potential issues that could show up but haven't yet, such as
versions with words in them (release candidates).

The packaging module is a high-quality library that provides a standard
version parsing algorithm, with which you can simply say "is this
version object greater than that one". Use it instead.

Fixes #1545

litex/soc/integration/builder.py

@@ -18,6 +18,8 @@ import subprocess
 import struct
 import shutil
 
+from packaging.version import Version
+
 from litex import get_data_mod
 from litex.gen import colorer
 
@@ -253,20 +255,18 @@ class Builder:
     def _check_meson(self):
         # Check Meson install/version.
         meson_present   = (shutil.which("meson") is not None)
-        meson_version   = [0, 0, 0]
+        meson_req = '0.59'
-        meson_major_min = 0
-        meson_minor_min = 59
         if meson_present:
-            meson_version = subprocess.check_output(["meson", "-v"]).decode("utf-8").split(".")
+            meson_version = subprocess.check_output(["meson", "-v"]).decode("utf-8")
-        if (not meson_present):
+            if not Version(meson_version) >= Version(meson_req):
+                msg = f"Meson version to old. Found: {meson_version}. Required: {meson_req}.\n"
+                msg += "Try updating with:\n"
+                msg += "- pip3 install -U meson.\n"
+                raise OSError(msg)
+        else:
             msg = "Unable to find valid Meson build system, please install it with:\n"
             msg += "- pip3 install meson.\n"
             raise OSError(msg)
-        if (int(meson_version[0]) < meson_major_min) or (int(meson_version[0]) == meson_major_min and int(meson_version[1]) < meson_minor_min):
-            msg = f"Meson version to old. Found: {meson_version[0]}.{meson_version[1]}. Required: {meson_major_min}.{meson_minor_min}.\n"
-            msg += "Try updating with:\n"
-            msg += "- pip3 install -U meson.\n"
-            raise OSError(msg)
 
     def _prepare_rom_software(self):
         # Create directories for all software packages.

setup.py

@@ -15,6 +15,7 @@ setup(
     license="BSD",
     python_requires="~=3.6",
     install_requires=[
+        "packaging",
         "pyserial",
         "requests",
     ],